WO2014021726A1

WO2014021726A1 - A process for purification treatment of waste water with a high content of metals, particularly copper and silver, and a composition for use thereof

Info

Publication number: WO2014021726A1
Application number: PCT/PL2013/000100
Authority: WO
Inventors: Wojciech Bal; Isabela ZAWISZA
Original assignee: Instytut Biochemii I Biofizyki
Priority date: 2012-08-03
Filing date: 2013-08-02
Publication date: 2014-02-06
Also published as: PL233402B1; PL400236A1; EP2917153A1

Abstract

The present invention relates to a method of purification of waste water with a high content of metals, especially Ag and Cu, and a composition for use in this method. The method for purification of waste water with a high content of metals, consists of two step process, wherein in the first step a mixture of at least two water soluble salts and a polymer that is biodegradable and has high molecular mass - chitosan are used. Then the process comprises filtering off the resulted precipitate and in the second step adding again chitosan to the filtrate.

Description

A process for purification treatment of waste water with a high content of metals, particularly copper and silver, and a composition for use thereof

The present invention relates to a method of purification of waste water with a high content of metals, especially Ag and Cu, and a composition for use in this method.

Background of the invention

Metal contamination of the waste water is a common environmental problem. Heavy metals are not biodegradable and are accumulated in living organisms, causing many diseases and health disorders of such organisms.

Copper is toxic in high concentrations. Copper poisoning leads to vomiting, cramps, convulsions, and even death. Therefore, according to the WHO recommendation an acceptable amount of copper in drinking water is 2 ppm (mg/kg). Compounds of silver also are toxic, and in high concentrations can cause argyria. The main sources of water pollution are steelworks, copper smelter, electroplating plants and glass industry. The presence of soluble silver ions in industrial waste water is a problem associated with the photographic industry, galvanizing plants, pharmaceutical and cosmetic industries. Due to the high value of metallic silver in the waste water, the attempts are being made for recovery thereof from waste water, see methods described by Lasko, L., Hurst, M.P., Environ. Sci. Technol., 33, (1 99), 3622 3626. Overview of methods used for purification of the waste water that contain metals (Ag, Cu) are presented in Table 1.

Table 1: Overview of methods used for the purification of waste water that contain Ag and Cu on the basis of Bartkiewicz B., "Industrial Wastewater", PWN, Warsa 2006, Lasko C.L., Hurst M.P., Environ. Sci. Technol., 33, (1999), 3622 3626, and Smith, A.L., Swiderska-Broz M., "Water Treatment", Oxford University Press, Wroclaw 2000.

Wan Ngah, W. S., Ghani, S. A., and Hoon, L. L. in Journal of the Chinese Chemical Society, 49, (2002), 625-628 describe adsorption as the preferred method for purifying of waste water containing metals (Ag, Cu). Adsorption technique is widely used because of its low cost and ease of implementation. Currently, as an environmentally friendly method for waste water treatment, biosorption is applied wherein non-toxic, natural substances are used as the sorbents.

Chitosan is a biopolymer with high sorption properties and ability to chelate metal cations due to the presence of free amino groups in its structure [Lasko et al. (1999)]. Chitosan is non-toxic, fully biodegradable and has a high biocompatibility. Chitosan can be easily modified by chemical reactions and physical processes, which leads to new derivatives of chitosan. Guibal E., in Separation and Purification Technology 38 (2004) 43 74, describes a modification of chitosan carried out in order to increase the sorbent affinity to metal (e.g. Cu) and the extension of the pH range in which the sorption may take place. The modification processes often comprise the crosslinking reactions of chitosan [WS Wan Ngah, L. C. Teong, M.A.K.M. Hanafiah, Carbohydrate Polymers 83 (201 1 ) 1446-1456]. Chitosan derivatives used in the recovery of copper are shown in Table 2. Chitosan is a compound absolutely non-toxic, so that its use, even on an industrial scale, does not cause environmental pollution. An important feature of this polymer is its biocompatibility. Further advantages comprise high adhesion and sorption capacity, high chemical reactivity and ability to chelate metals, because of the presence of a number of anchor groups on its surface. Due to the ability to receive multiple spatial conformation, chitosan can also capture the metal ions within its structure.

Table 2: Overview of the chitosan modification used in the recovery of copper from a ueous solutions.

Lasko et al. (1 99) describe chitosan also as a compound capable of chelating silver ions, but it was not used for purification of industrial waste water and other industrial wastes with a high content of Ag (I).

GB 2 364 047 discloses a composition for water treatment, and also for the purification of drinking water, comprising (i) an amino group-containing polysaccharide, for example chitosan, (ii) a second, more water-soluble polymeric material having an average molecular weight of at least 100,000, preferably a polyacrylamide. The composition can additionally comprise an inorganic metal salt selected from the salts: ferrous sulfate, ferric chloride, aluminum chloride, aluminum sulfate, manganese sulfate, manganese chloride, copper sulfate, copper chloride, or combinations thereof. The composition may further comprise a disinfectant. Polyacrylamide polymer is used as additional in the described composition. It is known that acrylamide is classified as carcinogenic material (material mutagenic category II). Thus, a use of polyacrylamide for purification of drinking water is associated with a risk of the water contamination with the monomer leading to the health hazard.

JP 9290231 describes a method for prevention of the leaching of heavy metals from the treated material. In this process metal was quenched with mixture of water, chitosan, and phosphoric acid and all the ingredients were kneaded with dust. However, this description comprises no mention of any introduction of such composition into the water in order to remove the metal from water. In particular, there is no mention of purifying water to a safe level for living organisms.

Therefore, there is still a need to develop a method for purifying metal- contaminated waste water, especially industrial waste water, such as from steel mills or mines, to reach the content of these metals at a level safe for living organisms, particularly humans. It is desirable that the method is carried out with environmentally friendly chemicals that do not cause further hazard to the environment and users of water purified this way.

Surprisingly a process for purifying waste water according to the invention, responds for such a need, thanks to the combination of chitosan with soluble inorganic salts in suitable proportions, which allows treatment of waste water with high content of copper and silver to the levels safe for living organisms.

General Description of the Invention

A method of water purification treatment involves a two-step process. In the first step effluents, particularly waste water with high acidity (pH = 3), are treated with a mixture of commercially available water-soluble salts especially phosphate(V) and sulfate(VI), and chitosan. Chitosan is practically insoluble in water, binding silver and copper ions, then in effect, its specific weight increases and it settles on the bottom of the container in the form of an insoluble metal complex. Silver (I) and copper (II) react leading to precipitation in result of forming a poorly water-soluble inorganic salts (Ag₂S044, Ag₃P0₄|, (¾(Ρ0 )₂|). Application of chitosan mixture with salts provides adequate viscosity and specific weight of the resulting precipitate. This precipitate can be easily filtered out. The resulting aqueous solution is colorless, clear, and is characterized by reduced acidity (pH ~ 6). The second step of this process provides ultimate cleaning of waste water to the level of metal content below 1 ppm. For this purpose an additional, suitable amount of the chitosan is used. After completion of the second step of the reaction the solution obtained by metal removal can be decanted from the precipitate and filtered. A clear, colorless and odorless filtrate is obtained with the metal content below 1 ppm.

Summary of the Invention

The invention relates to a process for purifying waste water with a high content of metals, comprising two steps. In the first step the mixture comprising a combination of at least two ions selected from the group consisting of: S0₄ ^2", P0₄ ^3~, Γ, Cl^~, and chitosan are added to the container filled with waste water, while maintaining the oxygen availability and mixing. Precipitate is filtered off, and then in the second step, chitosan is again added to the filtrate preferably chitosan is added in an amount of 10 g/1 to 150 g/1. Preferably ions selected from SO PO4^3", Γ, CI^" are added in the form of well water- soluble salts, comprising acid salts. In a preferred embodiment the ions selected from S0₄ ^2', P0₄ ^3", Γ, cr are added as ammonium salts, salts or acid salts of alkali metals, especially sodium or potassium. Preferably a combination of the salts SO₄ ^2", PO₄ ^3", selected from the group consisting of Na₂SC>₄, NaHSC>₄ and Na₂HP0₄, NaH₂P0₄, Na₃P0₄ is added_.

The invention is particularly suitable for the purification of waste water with a high content of copper and/or silver.

In the process according to the invention preferably the excess of SO4^2" ions in relation to Ag⁺ ions is used. More preferably the excess of SO4^2" ions in relation to Ag⁺ ions in ratio at least 1.1 : 1 molar equivalents, preferably in a ratio of 1.2: 1 molar equivalents is used.

Furthermore, according to the present invention excess of P<¾³⁺ ions in relation to Cu²⁺ ions is preferably used. More preferably the excess of P0₄ ³⁺ ions in relation to Cu²⁺ ions in ratio at least 1 ,1 : 1 molar equivalents, preferably in a ratio of 1 ,8:1 molar equivalents is used. Preferably chitosan is added in amount corresponding to 40%-90%, more preferably 50-80%, of the total mass weight of both salts used.

The present invention also provides a composition for the treatment of waste water with a high content of metals, comprising a mixture of well-soluble salts of acid radical SO4^2", P0₄ ^3', Γ, or CP, and chitosan, wherein the salts are in an excess of at least about 1.1 : 1 molar equivalents of the purified metal and chitosan is in an amount equivalent to 40%-90%, preferably 50-80%, of the total weight of each salt used. The composition contains preferably ammonium salts or acid salts of alkali metals, especially sodium salts, sodium acid salts, potassium salts or potassium acid salts. Preferably, the composition comprises a combination of salts having acid radical SO4^2", PO4^3", wherein salts are selected from the group consisting of Na S0₄, NaHS0₄ i Na₂HP04, NaH₂P0₄, Na₃P0₄.

The unexpected effect of the invention is shown in the figures below.

Figure 1 shows a UV-VIS spectra, taken in order to determine the concentration of copper ions in the obtained aqueous solution;

Figure 2 is a graph illustrating changes in the concentration of metals in the aqueous solution during the application of the procedure according to the invention;

Figure 3 is a graph showing the kinetics of removing silver(I) and copper(II) ions in reaction with a mixture of chitosan and soluble inorganic salts of phosphoric(V) and sulfuric(VI) acids;

Figure 4 is a graph showing the kinetics of removing silver(I) and copper(II) ions by chitosan in the second purification step.

The following the examples of the invention are presented. As used herein, the abbreviation eq means molar equivalent.

Example I

Comparison of the effects of individual components of the mixture separately and in mixture according to the invention.

Four identical samples of 5 ml aqueous solutions containing 35 g/1 of silver ions and 8 g/1 of copper ions were prepared. The first sample was treated as a reference sample. 0.22 g of chitosan was added to the second sample. A mixture of 0.28 g Na₂S0₄, 0.16 g Na₂HP0₄ (1.2 eq. S0₄ ^2" relative to Ag⁺ ions and 1.8 eq P0₄ ^3" with respect to Cu ⁺ ion) was added to a third sample. While a mixture of components prepared according to the invention (0.28 g Na₂S0 , 0.16 g Na₂HP0₄ and 0.22 g of chitosan) was added to the fourth sample. All samples were allowed to stand for 2 hours in the air while stirring. In all samples, except the control, part of the silver and copper ions present in the solution precipitated on the bottom of the vessel in the form of a water-insoluble precipitate. Samples were centrifuged and the aqueous solution was decanted from the above the color deposits. The solutions obtained in samples 2 and 3 had a light blue color. The solution decanted from the sample 4 containing a mixture of ingredients according to the invention was clear and colorless. In the resulting aqueous solutions the concentration of copper ions was evaluated using UV-VIS analysis and concentration of copper and silver ions were determined using ICP MS. The results are shown in Table 3.

Table 3: Results of the determination of copper ions using UV-VIS spectroscopy, and copper and silver ions using ICP MS in the resulting aqueous solutions.

The sample under assay Concentration of copper The concentration of ions in ions in solution [nig/1] as solution [mg/1] as measured determined by UV-VIS by ICP MS.

spectroscopy Ag Cu

1. The reference sample -8000 -35000 -8000

2. The sample after the 5900 12770 5771 chitosan addition

3. The sample after salt 2400 3683 2361 addition

4. The sample after no copper ions in the range 180 2,51 addition of the mixture of quantification i.e. < 7,94

according to the invention mg/kg is found In Table 3 data shows that the process according to the invention enables obtaining purified water with such a low content of metal ions Ag and Cu, respectively, as 180 mg/1 and 2.51 mg/1 (1CP MS) comparing to the use of chitosan alone, 12770 and 5771 mg/kg of solution, respectively. Adding the same salts alone for the metal precipitation also led to a satisfactory effect. This can be also seen on Figure 1 , which graphically shows the result of the UV-VIS analysis of copper ion concentration in the resulting aqueous solutions. Result of purification according to the present invention is shown by the solid line, which indicates virtually complete water purification from the copper ions.

Accordingly, it clearly results that the use of the method and the compositions of the invention leads to unexpected and very advantageous process for purification of water with high metal contents. Water purified with this method contains only trace amounts of metals, and therefore very pure samples of water are obtained, which would not be possible using the composition of each component separately.

At the same time in all experiments, in which for the purification of water contaminated with metal ions, S0₄ P0₄ ^", and chitosan were used, it was found that the sludge remaining after filtration can be easily removed, while the use of the salts alone led to the formation of a hardly removable precipitate which due to its microcrystalline nature gets between the pores in the frit funnel structure. This causes contamination of Schott funnel and partial penetration of the salt in the form of sediment into the filtrate.

On the other hand, use of chitosan alone, without any addition of salt does not lead to removal of the desired amount of metals from solutions.

Example II.

Purification treatment of wastewater containing 35 g 1 of silver ions, and 10 g I of copper ions, and at pH = 3

A process for purification of wastewater with a high content of metals (Ag, Cu) was developed and optimized at a laboratory scale. A sample of waste water containing 35 g/1 of silver ions and 10 g/1 of copper ions and pH = 3 was subjected to two steps of the purification process. In the first step, mixture of salts 0.28 g Na₂SC»4, 0.16 g Na₃P0₄ and 0.22 g of chitosan was added to 5 ml of waste water. Significant part of the copper and silver ions in the solution has been precipitated on the bottom of the vessel in the form of a water-insoluble precipitate. After filtration, a clear, colorless filtrate was obtained having reduced acidity (pH ~ 6). In a second step, the sample was purified by re-addition of chitosan in an amount of 50 mg, and the resulting precipitate was centrifuged. Results of a silver and copper ion determination in the solution after the first and second purification step is shown in Table 4 and in Figure 2.

Table 4: Results of ICP MS analysis of the metal content in the samples after the I and II purification step.

Metal The content of metal ions in the The content of metal ions in solution solution after the 1st purification after the 2nd purification step step [mg/kg] [mg/kg]

Ag 32 ± 0.09 4.00 ± 0.01

Cu 5.34 ± 0.08 1.34 ± 0.2

In the sample solution after the purification process of the invention the UV-VIS analysis showed no presence of copper in the obtained solution (copper concentration of <7.94 mg kg). ICP MS analysis showed the presence of metals at the level of 32 mg kg of silver and 5.34 mg/kg for copper. The addition at the second step 50 mg of chitosan, and then centrifuging the precipitate, enables to obtain the content of silver in the solution at the level of 4.00 ± 0.01 mg/kg, and copper - 1.34 ± 0.2 mg/kg. Increasing the amount of chitosan in the second step allows obtaining the levels for both metals of less than 1 mg/kg (1 ppm). These results showed that the first step of the process according to the invention leads to a very desirable levels of metals in the treated solution, while the second step comprising the addition of chitosan allows for an even more desired degree of purification of solutions of metal of order 1 ppm. So effective treatment of wastewater is extremely advantageous and the effect of the method and compositions of the invention was not possible to predict. Example III.

The kinetics of removal of silver and copper ions in the reaction with a mixture of chitosan and soluble inorganic salts of phosphoric (V) and sulfuric (VI) acids.

A sample of 5 ml aqueous solution containing 35 g/1 of silver ions and 8 g/1 of copper ions was prepared. A mixture of 0.28 g Na₂S04, 0.16 g Na₂HP04 and 0.22 g of chitosan was added to the sample. The sample was mixed vigorously. Part of silver and copper ions contained in the solution precipitated on the bottom of the vessel in the form of a water-insoluble precipitate. The sample was centrifuged, and sample of a small portion of the supernatant solution was collected for the analysis. The remaining solution and precipitate was allowed to stir open to the air. After 24 hours the precipitate was collected by centrifugation and another small portion of the supernatant solution was taken. The experiment was performed in duplicate. The collected samples were submitted for ICP MS analysis of content of silver and copper ions in solution. In this manner the kinetics of metal ions (Ag, Cu) removal in result of addition of the test mixture according to the invention was determined.

Table 5: Results of ICP MS anal sis.

Example IV.

The kinetics of removal of silver and copper ions by chitosan in a second purification step. To the sample of 5 ml aqueous solution containing 35 g/1 of silver ions and 8 g/1 of copper ions a salt mixture of 0.28 g Na₂S0₄, 0.16 g Na2HP0₄ and 0.22 g of chitosan were added. The sample was mixed vigorously.

Part of silver and copper ions contained in the solution has been precipitated on the bottom of the vessel in the form of a water-insoluble precipitate. The sample was centrifuged and the supernatant solution was decanted. Then, 50 mg of chitosan was added and the reaction mixture was centrifuged again. After centrifugation, a first small portion of the supernatant solution was collected. The residue was allowed to stir open to the air. After 48 hours the precipitate was again centrifuged, and a small portion of the solution was collected. The samples taken were submitted for ICP MS analysis for silver and copper ion content in solution. In this manner kinetics of metal ion (Ag, Cu) removal by chitosan was determined.

Table 6: Results of the ICP MS anal sis.

Example V

Testing of mixtures of chitosan and soluble salts of phosphoric acid (V) and sulfuric acid (VI) with different ratios of components.

Four samples of 5 ml aqueous solutions containing 35 g/1 of silver ions and 8 g/1 of copper ions were prepared. 0.28 g Na₂S04, 0.16 g Na₂HP0₄ (1.2 eq S0₄ ^2~ relative to Ag⁺ ions and 1.8 eq P0₄ ^" with respect to Cu ions) and 0.22 g of chitosan (50% by weight of the sum of the two added salt ) were added to the first sample. 0.28 g Na₂S0₄, 0.16 g Na₂HP0₄ (1.2 eq S0₄ ^2" relative to Ag⁺ ions and 1.8 eq P0₄ ^3" with respect to Cu^z+ ions) and 0.088 g of chitosan (20% by weight of the sum of both the added salts) were added To the second sample. 0.28 g Na₂S0₄, 0.16 g Na₂HP0₄ (1 .2 eq S0₄ ^2" relative to Ag⁺ ions and PO4^3" 1.8 eq with respect to Cu²⁺ ions) and 0.352 g of chitosan (80% by weight of the sum of both the added salts) were added to the third sample. To the fourth sample, 0.186 g Na₂S0₄, 0.089 g Na₂HP0₄ (0.8 eq S0₄ ^2" relative to Ag⁺ ions and P0₄ ^3~ 1.0 eq with respect to Cu²⁺ ions) and 0.138 g of chitosan (50% by weight of the sum of both the added salts) were added.

All samples were allowed to rest for 2 hours open to air while stirring. In each sample a portion of silver and copper ions contained in the solution precipitated, and settled on to the bottom of the vessel in the form of a water-insoluble precipitate. Samples were centrifuged and the aqueous solution was decanted from the above of the color deposits. The solutions obtained from the second and fourth sample had a light blue color. Solutions decanted from the first and third samples were clear and colorless. The resulting solution was analyzed by ICP MS.

Table 7: Results of the ICP MS analysis.

Example VI.

Comparison of the effect of a mixture of chitosan and phosphates (V) in the form of soluble salts with the effect of chitosan and phosphoric acid.

Four samples of 5 ml aqueous solutions containing 35 g/1 of silver ions and 8 g/1 of copper ions were prepared. 0.378 g Na₂HP0₄ (1.1 eq with respect to PO4^3" ions in the solution) and 0.22 g of chitosan (58% by weight added salt) were added to the first sample. To the second sample, 0.618 g NaaHPC (1.8 eq with respect to P0₄ ^3" ions present in the solution) and 0.22 g of chitosan (35% by weight added salt) were added. To the third sample, 0.154 ml of H3PO4 (1.1 eq with respect to PO₄ ^3" ions present in the solution) and 0.22 g of chitosan were added. To the fourth sample 0.252 ml of H₃PO4 (1.8 eq with respect to PO4^3" ions present in the solution) and 0.22 g of chitosan were added.

All samples were stirred. In samples wherein the phosphoric acid was added the viscous slurry sludge (sample III) was obtained and a sticky precipitate that was impossible to mix with a light blue solution of gel-sustained over the sediment (sample IV). Samples were subjected to centrifugation. The solutions derived from the first and second samples are transparent and clear (pH ~ 6.5). These solutions were analyzed ICP MS.

In case of the solutions containing phosphoric acid as an additive because of their high viscosity and a very acidic pH (pH = 1.1), MS ICP analysis was not performed.

Table 8: Results of the ICP MS analysis.

The experiment showed that the use of phosphoric acid instead of metal salts, in combination with chitosan leads to a very adverse effect consisting in obtaining a viscous suspension with a very low pH. However, using the same molar equivalents of salt in place of phosphoric acid leads to a surprisingly efficient purification of the water sample, leading to a few ppm of copper and 50 ppm silver. It needs to be noted that in this example, no further purification of the sample was used in the second step of the process according to the invention.

Claims

1. A process for purification of waste water with a high content of metals, comprising the steps of adding a mixture comprising a combination of at least two ions selected from the group consisting of SC ^2", PO4^3", Γ, CF, and chitosan to the waste water container, while maintaining the oxygen availability and mixing, filtering off the resulted precipitate and then in the second step adding again chitosan to the filtrate.

2. The process according to claim. 1 , wherein in the second step chitosan is added to the filtrate in an amount of 10 g/1 to 150 g/1.

3. The process according to claim 1 or 2, wherein the ions SO4^2", P0₄ ^3", Γ, Cl^¬ are added in the form of well water-soluble salts or acid salts.

4. The process according to claim 3, wherein the ions S0₄ ^", P0₄ ^", 1 , CI are added in the form of ammonium salts or acid salts of alkali metals, especially sodium salts, potassium salts.

5. The process according to claim 4, wherein the combination of the SO4^2', PO₄ ^3" salts is added, selected from the group consisting of N 2S0₄, NaHS0₄ and Na₂HP0₄, NaH₂P0₄, Na₃P0₄.

6. The process according to claims 1 -5, wherein the metal is copper or silver.

7. The process according to claim. 6, wherein an excess of S0₄ ^2" ions with respect to Ag⁺ ions is used.

8. The process according to claim 7, wherein an excess of S0 ^2" ions with respect to Ag⁺ ions in a ratio of at least 1.1 : 1 molar equivalents, preferably in a ratio of 1.2:1 molar equivalents is used.

9. The process according to claims 1-8, wherein an excess of P0₄ ³^ ions with respect to Cu²⁺ ion is added.

10. The process according to claim 9, wherein an excess of P0₄ ³⁺ ions with respect to Cu²⁺ ions in a ratio of at least 1.1 : 1 molar equivalents, preferably in a ratio of 1.8: 1 molar equivalents is added.

1 1 . The process according to claims 1 - 10, wherein the chitosan is added in an amount equivalent to 40% -90%, preferably 50-80%, of the total weight of each salt used.

12. A composition for treatment of waste water with a high content of metals, said composition comprising a mixture of at least two well-soluble salts of acidic residues S0₄ ²\ P0₄ ^3", Γ, CP, and chitosan, wherein the salts are in excess with respect to the treated metal of at least 1.1 : 1 molar equivalent and chitosan is in an amount corresponding to 40%-90%, preferably 50-80%, of the total weight of both salts used.

13. The composition according to claim. 12, wherein said composition contains ammonium salts or acid salts of alkali metals, especially sodium salts, sodium acid salts, potassium salts or potassium acid salts.

14. The composition according to claim. 13, wherein said composition comprises a combination of the salts of acidic residues S0₄ ^2", P0₄ ^3", selected from the group consisting of Na₂S0₄, NaHS0₄ andNa₂HP0₄, NaH₂P0₄, Na₃P0₄.